Contributions of magnetic structure and nitrogen to perpendicular magnetocrystalline anisotropy in antiperovskite ɛ−Mn4N

Abstract

To study how nitrogen contributes to perpendicular magnetocrystalline anisotropy (PMA) in the ferrimagnetic antiperovskite Mn4N, we examined both the fabrication of epitaxial Mn4N films with various nitrogen contents and first-principles density-functional calculations.Saturation magnetization (Ms) peaks of 110 mT and uniaxial PMA energy densities (Ku) of 0.1 MJ/m 3 were obtained for a N2 gas flow ratio (Q) of ~10% during sputtering deposition, suggesting nearly single-phase crystalline ε ε ε ε-Mn4N. Segregation of α α α α-Mn and nitrogen-deficient Mn4N grains were observed for Q ≈ 6%, which were responsible for a decrease in the Ms and Ku.The first-principles calculations revealed that the magnetic structure of Mn4N showing PMA was "type-B" having a collinear structure, whose magnetic moments couple parallel within the cplane and alternating along the c-direction. In addition, the Ku calculated using Mn32Nx supercells showed a strong dependence on nitrogen deficiency, in qualitative agreement with the experimental results. The second-order perturbation analysis of Ku with respect to the spin-orbit interaction revealed that not only spin-conserving but also spin-flip processes contribute 2 significantly to the PMA in Mn4N. We also found that both contributions decreased with increasing nitrogen deficiency, resulting in the reduction of Ku. It was noted that the decrease in the spin-flip contribution occurred at the Mn atoms in face-centered sites. This is one of the specific PMA characteristics we found for antiperovskite-type Mn4N. I. INTRODUCTIONPerpendicular magnetic anisotropy (PMA) in magnetoresistive devices such as magnetic tunnel junctions 1 has attracted significant attention in view of their potential application in spin-transfer torque (STT) magnetic random access memories. 2 Owing to their PMA with small saturation magnetization (Ms), Mn-based alloys with PMA such as D022-Mn3Ga, 3-6 D022-Mn3Ge, 7,8 and L10-MnAl 9-12 are regarded as satisfying the requirement for small critical STT-switching current density, Jc ∝ αMstHk (where α, t, and Hk denote the damping constant, ferromagnetic layer thickness, and anisotropy field, respectively), which is proportional to the PMA energy density (Ku). For example, the Ku and Ms values for sputter-deposited D022-MnGa films are reported to be ~1 MJ/m 3 and 310 mT, 3which are ~15% and ~20% of the values obtained for bulk L10-FePt, 13 respectively. First-principles density-functional calculations also predict that the spin-flip scattering process due to spin-orbit interaction is the key for PMA in the D022-Mn3Ga. 14 Mn4N with the ε phase has also long been known as a Mn-based PMA ferrimagnetic material with an antiperovskite structure described by the formula ANB3, where A and B correspond to Mn(I) 3 at corner sites and Mn(II) at face-centered sites, respectively (Fig. 1). 15 A neutron diffraction study identified a ferrimagnetic spin order with two distinct magnetic moments, 3.5 µB for Mn(I) and -0.8 µB for Mn(II), at 300 K. 16 The Mn4N films recently fabricated by spu...

Current-driven domain wall dynamics in ferrimagnetic Ni-doped Mn4N films : very large domain wall velocities and reversal of motion direction across the magnetic compensation point

“…1a. The total magnetic moment along the [001] quantization axis was found to be 1 µ B (Mn I: 3.3 µ B , Mn II : -0.8 µ B ) in good agreement with previous reports 48,49 . Ni doping in Mn 4−X Ni x N was taken into account using both the supercell approach and the coherent potential approximation (CPA) as implemented in SPR-KKR code [50][51][52] (see Methods for details).…”

Computing and Memory Technologies based on Magnetic Skyrmions

“…The intrinsic perpendicular magnetic anisotropy of Mn 4 N originates from unequal in-plane (a) and out-of-plane (c) lattice constants. The experimental c/a ratios of Mn 4 N thin films are close to 0.99, and K u less than 100 kJ/m 3 [71]. The measured M-H of 15 nm film in Fig.…”

Anomalous Hall and Nernst effects in ferrimagnetic Mn4N films: Possible interpretations and prospects for enhancement

“…The Mn4N films fabricated by sputtering and molecular-beam epitaxy (MBE) in previous studies exhibited Ms ≈ 0.1 T and Ku ≈ 0.1 MJ/m 3 . [14][15][16][17][18][19] While the AHE for Mn4N has been reported, 17,20) the ANE and AHE including the analysis from the perspective of intrinsic mechanism have not been studied so far.…”

“…The value of 0Ms was measured to be 100 mT, comparable to that of Mn4N films fabricated by sputtering and MBE. [14][15][16][17][18][19] The magnetization curves of sample-II are shown in Fig. 2…”